GNSS Receiver Application for Ionospheric Study

This chapter delves into the sophisticated subject of SDR (software-defined radio) Global Navigation Satellite System (GNSS) receiver applications for ionospheric research. It begins by discussing the formation of observables in navigation processors, including the enhancement of observables through coherent tracking and carrier smoothing techniques. The concept of differential observables is then explored in-depth, detailing single, double, and triple differences and addressing the ionospheric error in dual frequency GNSS receivers. A significant focus is placed on multi-frequency differential observables, examining techniques like widelane and narrowlane linear combinations and ionosphere-free observables. The chapter further extends to the application of multi-station network observables. It demonstrates how these observables can be interpolated to mitigate ionospheric influence and, conversely, how they can be utilized to derive detailed information about the ionosphere itself. In its final sections, the chapter presents the use of software receivers for ionospheric applications. This includes the monitoring of ionospheric scintillation, measurement methodologies, and the extraction of information on ionospheric irregularities. It highlights specialized applications such as software receiver use for scintillation measurements, research on the NavIC regional grid model, and airborne scintillation and total electron content (TEC) depletion monitoring, emphasizing the advantages of SDR receivers for the ultra-tightly coupled INS method.